Reverse cycle refrigerating system



A. B. NEwroN 2,498,861

REVERSE CYCLE REFRIGERATING sYs'rEu 3 Sheets-Sheet 1 Feb. 28, 1950 FiledFeb. 25, 1948 Feb. 2s, 195o 3 Sheets-Sheet 2 Filed Feb. 25, 1948 Feb.28, 1950 A. a. NEWTON 2,498,861

Rnvmsm wcm REFRIGERATING isv'sm Filed Feb. 25, 1948 3 Sheets-Sheet 3llraolufr Weasur Condenser is Ils. P

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rauf! Temp H- 5- XW WQ HM Patented Feb. 28, 1950 REVERSE CYCLEREFRIGERATIN G YSTE Alwin B. Newton, Dayton, Ohio, assignor to ChryslerCorporation, Highland Park, Mich., a

corporation of Delaware Application February 25, 1948, Serial No. 10,793

19 Claims.

'system a refrigeration system is employed to do the heating. Thedifference between a reverse cycle system and an ordinary refrigerationsystem for cooling is that in a reverse cycle system the heat dissipatedby the condenser is used for a useful purpose such as heating a room orheating water. In the ordinary refrigeration system it is the ability ofthe evaporator to extract heat from surrounding objects that is usedffor cooling some object. The evaporator of a reverse cycle system isexposed to some source of heat such as the outside air or ground or anoutside source of water and the heat picked up in the refrigerationsystem from the outside source is discharged from the condenser Iandserves to heat the building or water. The discussion herein will bedevoted to the appli-cationl of a reverse cycle system to the heating ofa building such as a home although it is to be understood that the heatmade available by the reverse cycle system may be used for any desiredpurpose.

If a reverse cycle system is designed to heat a particular residencethat'system must have a. capacity suilicient to heat the residence onthe coldest days. It has been found that the average seasonalrequirement is about 40% of the maximum requirement in a typicallocality due to the fact that the most extreme heating requirements donot exist on the milder days. Heretofore, systems of xed compressordisplacement capacity have been used to heat residences throughout theseason in which climatic changes produce diierent demands for heat.Controls have been used to regulate the time of operation of thesesystems but the compressor displacement capacity has remained constant.It is a principal object of this invention to provide a means for morethan doubling the efciency of such a system by unloading individualcompressor cylinders to adapt the system to the heating requirementsinstead of running the system at full compressor displacement capacityfor short intervals. This increase in eiliciency is obtained byproviding an automatic control of the compressor compression ratio sothat the mean temperature differences between the refrigerant and theheat source and the refrigerant and the substances to be heated arealways at a minimum. Appreciable reductions in compression ratio areobtained thereby which greatly improve the overall eiiiciency duringlight load periods. 1

Some suggestions to overcome the problem presented by systems of xedcompressor displacement capacity have contemplated the use of systems ofsmall capacity and the heating of water in a water tank during mildweather and using this stored heat to heat the house during the periodswhen the refrigeration system lacks sufficient capacity. This system isimpractical for tremendous quantities of water are involved. It is muchmore desirable to provide a system of suiiicient -capacity and to unloada portion of the system when all of the capacity is not required.

One type of reverse cycle system or heat pump has the evaporator exposedto the atmosphere to extract heat therefrom. This type of system hasIcertain inherent advantages relating to its installation. However, italso presents additional diiculties. In view of the fact that thefunction of the evaporator is to extract heat from the atmosphere it isevident that when the outside temperature increases the system has itsgreatest heat extracting capacity. Unfortunately this is just thereverse of what is desired, for the greatest demand for heat exists whenthe outside temperature is low and at this time with present systems ofthis type the capacity of the system to obtain heat is lowest. It is anobject of this invention to provide means for adjusting the capacity ofa reverse cycle system and to provide in this means a recognition of thechanges in its capacity.

The volume of air delivered by either system is determined by therequirement for 'air at the established delivered air temperature underextreme conditions. The temperature of the delivered air in theconventional system increases as the load decreases or outsidetemperature increases. Since the system operates under what may betermed a partial load for the major portion of the season the deliveredair temperature of a conventional system is greater than necessary mostofthe time and itis axiomatic that/"as the delivered air temperatureincreases the eiiiciency of the system decreases. In contrast to this ina system operating in accordance with my invention the delivered airtemperature may be decreased as the load on the system decreases (i. e.outside temperature increases). Throughout the major portion of theseason when partial load conditions prevail the temperature of deliveredair is therefore less with my invention than in a conventional systemand therefore the season average of the eiiiciency is greater. 'I'hevolume of air delivered per unit of time by either system is constantfor that system throughout the season but this volume may be establishedat a lower value in a system incorporatlngmy invention for a higherdelivered air temperature may be used under extreme load conditionswithout significantly penalizing the efficiency of the system under themore frequent partial load -conditions.

In addition, discussions heretofore made involving heat pumps andreverse cycle systems have considered the advisability of using thesystem for heating during winter months and cooling during summermonths. This produces an additional problem in view of the fact that thesystem and particularly the compressor of the system will havealtogether too much cooling capacity compared to the heating capacityrequired to handle a given installation. For example, a 5 H. P.compressor might be required to provide the necessary B. t. u. outputfor heating a particular residence whereas only a2 H. P. compressorwould be required to cool the same residence. It is an additional objectof this invention to provide a means for varying the capacity of thesystem between summer and winter requirements.

It is a further object of this invention to provide a reverse cyclesystem or heat pumpwith a compressor unloading means therein and toprovide means for utilizing the refrigerant pressure within the systemto operate the unloading means.

It is van additional object of the invention to provide a heat pump orreverse cycle system having a variable capacity compressor therein andcontrol means to vary the capacity of the compressor in response tooutside temperature and delivered air temperature conditions. Ifdesired, a supplemental control mas7 be associated with the system toinitiate the operation of the system in response to a room temperaturethermostat.

It is a further object of the invention to improve the electrical loadcharacteristics of a reverse cycle heating system. It is.recognized thatan electrical power supply company nds a reduced load operating for arelatively long length of time to be more acceptable than a relativelyhigh load imposed for short intervals. Varying the capacity of thecompressor rather than varying the time of operation of a compressor ofxed capacity accomplishes this.

These and other objects of my invention will become apparent from thefollowing description taken in conjunction with the accompanyingdrawings in which:

Fig. l is a diagrammatic showing of a heating system for a residenceincorporating my invention;

Fig. 2 is an elevation, partly in section of a compressor having anunloader means incorporated therein;

Fig. 3 is an enlarged fragmentary section of a portion of the Fig. 2compressor unloader means;

Fig. 4 is a vertical sectional view of a control ""f'adapted-tobeincorporated in the rev@rse Cycle Fig. 6 comprises 3 charts from whichcomputations showing the relative eiciency of a conventional system anda system incorporating my invention will be made where these systemsutilize an evaporator coil exposed to the atmosphere.

In Fig. l a residence I0 is illustrated as having a room I2 thereinwhich is to be heated by a reverse cycle refrigerating system. A hot airdischarge grille I4 and a cold air return grille I6 are illustrated asbeing connected by a duct I8. A fan 2D is positioned in the duct toinduce the circulation of air therein. The condenser 22 of a reversecycle refrigeration system is also located in the duct I8 so that aircirculating therein is heated by passing through the condenser 22. Theair from room I2 is thus recirculated and heated by the condenser 22.

The reverse cycle refrigerating system which provides heat to thecondenser 22 comprises a compressor 2li having unloading means 26associated therewith, an expansion valve 28 and an evaporator coil 3B.The evaporator coil 30 may either be located in the air outside of thebuilding I or be buried in the ground adjacent the building Ill.Refrigerant is conveyed from the evaporator 36 to compressor 2li by line32. The compressed refrigerant is delivered from compressor 24 tocondenser` 22 by lines 34 and 35 and conveyed from condenser 22 to theexpansion valve 28 by a line 38. The unloading means 25 to be describedherein receives compressed refrigerant from compressor 24 through lines36, dil, and 4I. The passage of refrigerant to unloading means 26through lines 3G and li is regulated by a control means generallydesignated by the numeral @2. The control 'means 52 operates in responseto a temperature bulb 236 located in the duct l@ and temperature bulbLIS located outside the building Ill and throttles the supply ofrefrigerant to unloading means 2t in response to conditions measured bythe bulbs lli and 65. A line i3 having a restriction I5 therein isprovided to bleed refrigerant from unloading means 2t to suction line32.

If desired a supplemental control may be provided to initiate andterminate the operation of the compressor 24 in response to roomtemperature conditions. Electric energy to operate the compressor 24 isprovided by an electrical line 48 and an electrical line 50. Theelectrical line 5G contains a switch 52 which is opened by a spring 54and closed by a solenoid 5B. The solenoid 56 is wired in series with asource 58 of low voltage electric energy and a room temperatureresponsive thermostat switch 60. When the room temperature responsivethermostat 60 demands heat the switch (not shown) therein is closed andthe electrical circuit between source 58 and solenoid 56 is closed.Energization of solenoid 56 closes switch 52 which completes theelectrical circuit to compressor 24. Although means will be describedherein for controlling the delivery of heat by the system in response tooutside temperature conditions the supplemental room thermostat controlis desirable for it is able to compensate for conditions such as whetherthe day is sunny or cloudy or whether a high wind is blowing. In otherwords, control 42 determines the capacity of the system during eachoperating period, bul the duration of the operating period is determinedby thermostat 60.

Referring to Figs. 2 and 3 the construction 'o1 the compressor 24 andthe unloading means 2E may be seen in greater detail. The compresso] 75unloading means illustrated herein is describe:

in greater detail in my application, Serial No. 792,277, tiled December17, 1947, as a continuation in part of application, Serial No. 825,864,filed October 31, 1945, now abandoned. Compressor 24 comprises anelectric motor 82 which drives a compressor crankshaft 64 to which areconnected a plurality of connecting rods 66 each operating a piston 68in a cylinder 10. A suction manifold 12 in the compressor is connectedto the line 32 by an orifice (not shown). Re-

frigerant passes into the interior of each of the.

cylinders through a suction valve 14 and is ejectedthrough a dischargevalve 16 into a discharge passage 18 operatively connected to the line34 by an orifice. Details of the valve and piston construction may beascertained from the Patent No. 2,137,965, which issued on November 22,1938, and the Patent No. 2,185,473 which issued on January 2, 1940, toCharles R. Neeson.

The suction manifold 12 is connected through` ports 80 with the interiorspace 82 of the compressor crankcase containing a flexible metallicbellows 84. Bellows 84 is thus subjected to the pressure of expandedrefrigerant vreturned from the evaporator 30. Movement of the Abellows84 which has an end piece 86 welded to a link rod 88 causesreciprocation of the link rod 88 which is connected by rocking levers 90to a master valve member 92 contained in a master valve 93. The mastervalve member 92 is provided with a plurality of notches 94 so thataspring pressed ball 96 engaging in the notches permits step by stepmovement of the master valve member. Each step causes one of a pluralityof slots 98 to be connected to or disconnected from a source of oilpressure in an oil pressure tube |00. Each of the slots 98 is connectedto a short tube |02 leading to a cylinder |04 (Fig. 2) in which ismounted a spring loaded `unloader piston |06 connected to an unloadingmechanism including a yoke |08 adapted to ride on a ramp ||0 and to bemoved axially of piston 68 as the piston |06 moves the yoke |08longitudinally. The yoke causes axial movement of a collar ||2 havingunloader pins ||4 mounted thereon which when moved axially causes thesuction valve 14 to be held open continuously whereby the cylinder isunloaded. The position of the movable valve part 92 therefore controlsthe number of unloader pistons i06 to which oil pressure is applied andhence controls the number of cylinders in operation. When -as disclosedin Fig. 2 all but one of slots 98 are connected to tube |00 through theannular space surrounding a reduced portion of valve member 92 all butone of the individual cylinders will be loaded or operating. When valvemember 92 is moved to the left by the length of another notch 94 twocylinders will be unloaded since another one of the unloader cylinders|04 will be disconnected from the source of oil pressure.

Oil pressure is applied to the unloader mechanism through the mastervalve from Aa pressure lubrication pump (not shown) details of which maybe ascertained from the aforesaid Patent No. 2,185.473. The oil pressurepump operates coextensively with the operation of motor 62 so that nooil pressure will be supplied to the master .valve unless the motor isoperating and since it takes a short while for the pressure to be builtup by the oil pump it is apparent that all cylinders will be unloadedduring starting thereby preventing large starting current demand. It isalso apparent that after oil pressure is available a number of cylindersmay be unloaded depending upon the position of the link rod 38.

The position of link rod 88 may be controlled by the degree ofcompression of the flexible metallic bellows 84 which compression iseffected by the pressure of the refrigerant in the space 82 connected tothe suction side of the refrigerating system through the port 80. Thepressure of the gas against bellows 84 operates against a compressionspring ||8 positioned between the end of the bellows and a disc Ill. Thedisc has wings |20 at opposite sides projecting through a slot in athreaded sleeve |22. The sleeve is secured as by welding to an aperturedmember |24 to which the bellows 84 is secured. A nut |28 threaded on thesleeve |22 determines the position of the disc ||8 and consequently thecompression of the spring H6. The link rod 88 has a reduced outer end onwhich is threaded a nut |28 serving to guide the rod in sleeve |22. Alock nut |30 retains the nut |28 in position. An additional light springmay be provided to react between nut |26 and nut |28. 'I'his facilitatesan adjustment of the spring pressure opposing compression of bellows 84since springs ||8 and |3| oppose each other. The resultant spring forcecontrols the unloading pressure of the master valve 93 so that thesuction pressure of the refrigerating system may be controlled withinreasonable limits.

In addition to the use of suction pressure to determinev the compressorunloading additional V means for unloading the compressor in response totemperature of the heated delivered air and the outside temperature areprovided. A housing. |32 is secured in fluidtight relationship toapertured member |24. A collar |34 is threaded on housing |32 and a dome|36 is secured as by welding to the collar |34. An orifice |38 isprovided in housing |32 and has connected thereto the line 4| adapted toconduct refrigerant to the interior of the housing |32 and dome |36 sothat the pressure Voi' this refrigerant may act upon the interiorof thebellows 84. Thus on the exterior'of the bellows 84 the suction pressuretends to compress the bellows. From the interior of the bellows 84 thespring ||6 and the pressure of refrigerant supplied by line 4| aretending to expand the bellows 84. The resultant of these forces actingon the bellows 84 will determine the degree of compression thereof andthereby determine the position of the link rod 88 and the master valvemember 92 which in turn determines the number of cylinders of compressor24 which are loaded. The refrigerant permitted to enter unloading means26 from line 4| is controlled by a control 42. The line 43 bleedsrefrigerant from dome |36 and thereby permits the pressure within dome|36 to decrease when the supply from line 4| is restricted. The line 43is provided with a restriction and the capacity of this bleed line 43 isless than the capacity of line 4| so that pressure may be built up indome |36 when the line 4| is not restricted by control 42.

The control 42 is adapted to throttle the supply of refrigerant fromline 34 of the compressor 24 through the lines 40 and 4| to theunloading means 26. A control means similar to the lcontrol 42 used fora different application is illustrated in my copending application,Serial No. 763,596, filed July 25, 1947. The lines 40 and 4| conductingrefrigerant from compressor 24 to compressor unloading means 28 have thecontrol 42 positioned between them. The control 42 serves as a valvegoverning the passage of.

refrigerant from line`40 to line 4|.

The control 42 is mounted in a housing |66 having openings in which thelines 40 and 4| are received. A dome |18 is secured to a side wall ofthe housing |68 over an opening |1| therein. A pressure responsivebellows |12 is positioned within the dome and cooperates therewith toform a liquidtight compartment |14. The bulb 46 previously referred tois connected to compartment |14 and the compartment |14 and bulb 46 arelled with an expansible medium such as one of the liquids commonlyemployed for this purpose. Temperature changes will cause the medium inthe bulb 46 to expand and activate the bellows |12. The bulb 46 ispositioned outside the building |0 as illustrated in Fig. 1 and exposedto the atmosphere. A rod |16 is adjustably secured to the bellows. AnL-shaped lever |18 is pivoted at |80 and has one leg thereof adapted tobe engaged by the rod |18. Movement of the rod |16 rotates the lever |18about the pivot |80 against the spring 8| to be described. The other legof the lever |18 has a valve element |82 in theform of a pad secured tothe end thereof. `Valve element |82 is positioned in a predeterminedposition for each outside temperature bythe apparatus described.

A similar Amechanism is'provided to control the position of a secondvalve element |84. A dome |86 is associated with the housing |68 andcontains a bellows element |88 which cooperates with the dome |86 toprovide a liquidtight compartment |90. The compartment |90 is connectedto the bulb 44 which was previously referred to and the bellows |88 isactivated by expansion and' contraction of a medium provided in thecompartment |90 and bulb 44. Bulb 44 is positioned in the heated airdelivery duct I8 as shown in Fig. l. A lever |92 carrying valve element|84 is pivoted on the housing |68 at |94. The spring |8| tends toseparate levers |18 and |92 While movements of the bellows elements tendto move the levers toward each other. A lever |96 is pivoted on thehousing |68 at |98. A plate member 200 is also pivoted `at |98. Athreaded ele-= ment 204 is positioned between levers |92 and |96 and inengagement with these levers. The threaded element 204 is threaded uponan adjusting rod 208 carried by the plate member 200. A knob 208 isprovided on rod 206 for manual adjustment thereof. A rod 2 0 isoperatively connected to the bellows |88 and adapted to engage the lever|96 in response to contraction and expansion of the bellows |88. Meansare thus pro-v vided to position the valve element |84 in apredetermined position for each temperature in the duct |8. The'valveelement |84 is connected by a flexible tube 2|2 to the line 40. It willthus be seen that the valve element |82 when properly. positioned canclose the tube 2|2 so that refrigerant cannot be emitted therefrom. Whenvalve |82 is positioned away from valve element |84 so that refrigerantmay escape from line 40 and tube 2|2 the housing |68 is filled withrefrigerant which entersline 4| and is transmitted thereby to unloadingmeans 26. A modulating control is thus provided. The supply ofrefrigerant to the unloader control means 26 is thus dependent upon bothoutside temperature conditions and the temperature of the air, in theduct I8 which are measured by the bulbs 46 and 44 respectively. Althoughrefrigerant has been described as the medium delivered by pipe 4| tocontrol the unloading of the compressor cylin;

8. ders it ls to be understood that a source of compressed air could besubstituted so that the air supply to the unloading means 26 would bemodulated by control means 42. A system using an air supply to operatethe unloader means is illustrated in my copending application Serial No.792,277 referred to above.

As previously explained in setting forth the objects of my invention theoutside temperature dictates the requirement for heat and when anevaporator exposed to the atmosphere is used the capacity of the systemto absorb heat is also a function of the outside temperature. Both ofthese factors are therefore important in selecting the optimum capacityof the compressor which is accomplished by unloading means 28. Inaddition, the temperature of air in duct I8 is directly related to theability of this 'air to heat the room I2 and therefore the capacity ofcompressor 24 has been controlled so that its capacity is suiiicient atall times to provide a satisfactory temperature of heated air in ductI8.

Changes in the condition of the heat source areautomatically-compensated for by the apparatus described herein. Forexample, where an evaporator exposed to the atmosphere accumulates frostor Where long continuous operation of a ground coil lowers thetemperature of the ground in the vicinity of the coil the ability of aconventional reverse cycle system to deliver heat is impaired. Incontrast to this the controls described herein automatically adjust thesystem to compensate for this change in the condition of the heatsource. This change induces a drop in compressor suction pressure whichis followed by a drop in compressor discharge pressure and temperaturewhich in turn drops the delivered air temperature which activates bulb44 which automatically loads the compressor to compensate for this. Thecompressor loading as described herein is therefore controlled inresponse to four conditions which include the outside air temperature,the delivered air temperature, the condition of the heat source asexplained above, and the room temperature by the thermostat 68.

In Fig. 5 charts have been illustrated which facilitate a comparison ofthe efoiency of a reverse cycle heating system controlled by an onoffthermostat and a system incorporating my invention in which thecompressor displacement capacity may be varied. Both of these systemshave the evaporator buried in the ground. The chart on the left labelledconventional system shows the ground at a temperature of F. as the heatsource. Under heavy load conditions a reasonable evaporator temperaturewould be approximately 20 F. which corresponds to 37 pounds absolutepressure. To produce a room temperature under extremely cold conditionsthe delivered air temperature would be about F. and this would require acondenser temperature of about F. which corresponds to 194 poundsabsolute pressure. The efficiency or power requirements of the systemare related to the absolute pressures of the refrigerant in the systemVbecause the density of the ,refrigerant increases as its absolutepressure increases and therefore, a greater weight of refrigerant willbe compressed as the density increases. By consulting tables familiar tothose skilled in the art it may be seen that .124 H. P. per thousand B.t. u.s per hour of operation of the heating A apparatus would berequired for this conventional It is estimated for a typical localitythat the average of the heating requirements over the period of a seasonapproximate 40% of the maximum requirements under extreme conditions. Byvarying the capacity of the system advantage may be taken of this fact.Referring to the chart in Fig. 5 labelled Variable capacity system" thesystem has been illustrated as operating at its usual or average loadwhich is only 40 per cent of its potential capacity. The averagedelivered air temperature is considerably lower and the averagecondenser temperature and pressure are lower while the averageevaporator temperature is higher than in the conventional system chart.Note that the disadvantage in the conventional system was that its timeof operation could be controlled but its capacity was always thatrequired for extreme conditions. Reference to the tables previouslyreferred to disclosed that the average horsepower requirement for theseason for the variable capacity system is .054 H. P. per thousand B.'t.u.s per hour of operation. Therefore, over the period of a season thevariable capacity system requires only about forty-three per cent of thepower or electrical energy that the conventional system requires.

In Fig. 6 a similar set of charts have been illustrated for systemsusing evaporators exposed to the atmosphere. In view of the fact thatchanges in outside temperature affect the eiliciency of the conventionalsystem of this type, this system has been shown with anoutsidetemperature of F. and an outside temperature of 40 F. 'I'he outsidetemperature of 40 F. has been used as illustrative of the average oftemperature conditions which might be obtained in certain localitiesover the period of a season while the 0 F. has been used as illustrativeof extreme conditions for which the apparatus must be designed. Bycomputations similar to that explained with reference to Fig. it is seenthat the horsepower requirements vary between .18 H. P. per thousand B.t. u.s per hour for operation at 0 F. and .218 H. P. per thousand B. t.u.s per hour for operation at 40 F. In the latter case the absolutepressures are greater and the capacity of the system cannot be variedand therefore the efdciency of the system is lower. By contrast to thisthe Variable capacity system operating at its seasonal average of 40% ofits capacity or 40 F. uses .057 H. P. per thousand B. t. u.s per hour.The savings in energy consumption produced by varying the capacity ofthe system are thus of major proportions and constitute an unanticipatedresult obtained by the modiiication of the reverse cycle system asdescribed herein.

The charts of Figs. 5 and 6 illustrate the fact that with my improvedcontrol the temperature difference between the refrigerant in theevaporator and the heat source and the temperature difference betweenthe refrigerant in the condenser and the substance to be heated aresimultaneously controlled so that each of these temperature differencesare maintained at the minimum value compatible with the requirement forheat.

I claim:

1. In a reverse cycle refrigeration system having an evaporator locatedin heat transfer relation with a source of heat, a condenser located inheat transfer relation with a substance to be heated and a compressor,unloader means to vary the capacity of said compressor and controlapparatus responsive to conditions indicating the available heat in saidsource and the demand for heat by said substance to control saidunloader means and thereby adjust the capacity of said system so that itoperates at its optimum efliciency for said conditions.

2. In a reverse cycle refrigeration system having an evaporator locatedin heat transfer relation with a source of heat, a condenser located inheat transfer relation with a substance to be heated and a compressor,unloader means to vary the capacity of said compressor and controlapparatus responsive to the temperature of said source and thetemperature of said substance to control said unloader means todetermine the number of operating cylinders in said compressor tothereby adjust the capacity of said system so that it operates at itsoptimum efficiency.

3. In a reverse cycle refrigeration system adapted to heat a space in a,building by extracting heat from a natural source outside of saidbuilding, a compressor, a cylinder unloading mechanism associated withsaid compressor and adapted to vary the capacity thereof by determiningthe number of loaded cylinders in said compressor and control mechanismresponsive to temperature changes outside of said building to controlthe operation of said unloading mechanism whereby the capacity of saidcompressor is at all times a function of the temperature outside of saidbuilding.

4. In a building having a space to be heated and a, duct for heated airto heat said space, a reverse cycle refrigeration system to heat air insaid duct comprising a condenser located in heat transfer relationshipwith said air, an evaporator adapted to assimilate heat from a sourceoutside of said building, a refrigerant compressor, a cylinder unloadingmechanism associated with said compressor and adapted to reduce thecapacity of said compressor by unloading individual cylinders thereofand control means responsive to the temperature outside of said buildingtocontrol the operation of said unloading mechanism so that thecapacityof said compressor is at all times a function of the temperatureoutside of said building.

5. In a building having a space to be heated and a duct for heated airto heat said space, a reverse cycle refrigeration system to heat air insaid duct comprising a condenser located in heat transfer relationshipwith said air, an evaporator adapted to assimilate heat from a sourceoutside of said building, a refrigerant compressor, a Lcylinderunloading mechanism associated with said compressor and adapted toreduce the capacity of said compressor thereof, control means responsiveto the temperature outside of said building and to the temperature ofheated air in said duct to control the operation of said unloadingmechanism so that the capacity of said compressor is at all times afunction of said temperatures.

6. In a refrigeration system, means forming a circuit for refrigerant insaid system, a multi-cylinder compressor interposed in said circuit,unloader mechanism associated with said compressor and adapted to unloadindividual cylinders of said compressor and control means for saidunloader mechanism including a path for said refrigerant forming aportion of said circuit, said control means being adapted to regulatethe ow of refrigerant in said path and to deliver said regulated flow ofrefrigerant to said unloader mechanism to control the latter.

7. In a reverse cycle refrigeration system having an evaporator locatedin heat transfer relation with a source of heat. a condenser located inheat transfer relation with a substance to be heated, a compressor andmeans forminga circuit for refrigerant through said evaporator, saidcompressor and said condenser, unloader means interposed in said circuitto vary the capacity of said compressor in response to the pressure ofrefrigerant supplied to said unloader means and control means adapted tothrottle the supply of refrigerant to Said unloader means in response tooutside atmosphere temperature and in response to temperature of thesubstance to be heated.

8. In a reverse cycle refrigeration system hav- :lng an evaporatorlocated in heat transfer relation with a source of heat, a condenserlocated in heat transfer relation with a substance to be heated and acompressor, unloader means to vary y the compression ratio of saidcompressor and control apparatus responsive to outside temperature andto the demand for heat to control said unloader means and thereby adjustthe compression ratio of said compressor.

9. In a reverse cycle refrigeration system adapted to heat a space in abuilding by extracting heat from the outside atmosphere, an evaporatorexposed to said atmosphere, a condenser located in heat transferrelation with respect to said space, a compressor, unloader means tovary the capacity of said compressor and control apparatus associatedwith said unloader means and adapted to operate said unloader means inresponse to changes in the capacity of said system to absorb heat fromthe atmosphere. v

10. In a reverse cycle refrigeration system having an evaporator locatedin heat transfer relation with a source of heat, a condenser located inheat transfer relation with a substance to be heated, a compressor andmeans forming a circuit for refrigerant through said evaporator,condenser and compressor, unloader means to vary the capacity of saidcompressor and ,control apparatus adapted to maintain the meantemperature dierential between said refrigerant and said source and saidrefrigerant and said substance at a predetermined minimum.

i1. In -a reverse cycle refrigeration system adapted to heat a space andhaving an evaporator located in heat transfer relation with a source ofheat, a condenser located in heat transfer relation with a substance tobe heated and a compressor, unloader means to vary the capacity of said"compressor, control apparatus responsive to conditions indicating theavailable heat in said source and the demand for heat by said substanceto control said unloader means and thereby adjust the capacity of saidsystem and supplemental space temperature responsive ,control meansadapted to initiate and terminate operation of said compressor inresponse to space temperature conditions whereby the capacity of saidsystem during each operating period is established by said controlapparatus and the duration and frequency of the operating periods arevdetermine by said supplemental control means. f

12'. In a reverse cycle refrigeration system adapted to heat a space andhaving an evaporator located in heat transfer relation with a source ofheat, a condenser located in heat transfer relation with a substance tobe heated and a compressor, space temperature responsive control meansto initiate and Vterminate operation of said compressor and controlapparatus responsive to the temperature of air delivered to said spaceto control the capacity of said system during each operating period ofsaid compressor so that the heat supplied by delivered air during eachoperating period will equal or exceed the demands of the space.

13. In a reverse cycle refrigeration system adapted to heat a space andhaving an evaporator located in heat transfer relation with a source ofheat, a condenser located in heat transfer relation with a substance tobe heated and a compressor, space temperature responsive control meansto initiate and terminate operation of said compressor and controlapparatus responsive t0 the outside temperature to control the capacityof said system during each operating period of said compressor so thatthe heat supplied by said system to said space during each operatingperiod will equal or exceed the demands of the space for the existingoutside temperature conditions.

14. In a reverse cycle refrigeration system adapted to heat a space andhaving an evaporator located in heat transfer relation with a source ofheat, a condenser located in heat transfer relation with a substance tobe heated and a compressor, unloader means to vary the capacity of saidcompressor and control apparatus adapted to control said unloadermechanism so that the heat discharged by said system to said space issubstantially constant when the ability of said evaporator to obtainheat decreases, said control apparatus being adapted to cause saidunloader means to increase the loading of said compressor to maintainthe discharge of heat by said system at a constant value during auniform weather condition.

15. In a space heating apparatus utilizing a reverse cycle refrigerationsystem to obtain heat outside said space and to deliver said heat tosaid space a refrigerant compressor, cylinder unloading mechanismassociated with said compressor and control apparatus to control saidunloading mechanism, said control apparatus including means to controlsaid unloading mechanism in response to changes in the temperature 0fair dey livered to said space to compensate for changes in the abilityof said system to absorb heat from the outside, means to control saidunloading mechanism in response to changes in temperature outside ofsaid space, and supplemental space temperature responsive control meansto initiate and terminate the operation of said compressor in responseto changes in the temperature of said space.

16. In a reverse cycle refrigeration system adapted to heat a space in abuilding by extracting heat from a natural source outside of saidbuilding and vheating air from said space, a compressor, a cylinderunloading mechanism associated with said compressor and adapted to varythe capacity thereof by determining the number of loaded cylinders insaid compressor and control mechanism responsive to the temperature ofsaid heated air to control the operation of said unloading mechanism.

1'7. In a building having a space to be heated and a duct for heated airto heat said space, a reverse cycle refrigeration system to heat air insaid duct comprising a condenser located in heat transfer relationshipwith said air, an evaporator `adapted to -assimilate heat from a sourceoutside of said building, a refrigerant compressor, a cylinder unloadingmechanism associated with said compressor and adapted to reduce thecapacity of said compressor by unloading individual cylinders thereof,and control means responsive to the temperature of air in said duct tocontrol the operations of said unloading mechanism so y.that thecapacity of said compressor isat all times aiunction-of the temperatureof air in said duct whereby the effect of outside conditions` on-saidsystem is automatically compensated for by adjusting the capacity of thesystem to produce an optimum delivered air temperature.

18. In a reverse cycle refrigeration system including an evaporator forrefrigerant located in heat transfer relation with a source of heat andadapted to receive heat by virtue of a first temperature differentialbetween said refrigerant and said source, a condenser for refrigerantlocated in heat transfer relationship with asubstance to be heated andadapted to deliver heat 'to said substance by virtue of a secondtemperature differential between said refrigerant and said substance, acompressor to pump heat and refrigerant from said evaporator to saidcondenser, cylinder, unloading mechanism associated with said compressorand control mechanism to control said unloading mechanism so that the,said ilrst and second temperature diierentials are maintained at theminimum values capable of delivering the required heat to saidsubstance.

19. In a building 4having aspace to be heated and a duct for heated airto heat said space, a reverse cycle refrigeration system to heat air insaid duct comprising a condenser located in heat REFERENCES C ITED Thefollowing references are of record in the file of this patent:

UNITED STATES PATENTS v Number Name Date 1,969,076 Hirsch Aug. 7, 19342,122,012 Smith June 28, 1938 2,185,473 Neeson Jan. 2, 1940 2,296,304Wolfert Sept. 22, 1942 2,296,822 Wolfert Sept. 22, 1942 2,313,390 NewtonMar. 9, 1943 FOREIGN PATENTS Number Country Date 173,493 SwitzerlandNov. 30, 1934

